1. Field of the Invention
This invention relates to a print actuator assembly, and more particularly relates to a print actuator assembly having, for each print position, and end-pivoted lever print hammer and a pivoted bellcrank armature which urges the hammer to free flight by energy transfer at an energy transfer contact surface, the armature pivot, print hammer pivot and energy transfer surface being aligned in sequence, coplanar and dimensionally interrelated for effective operation and minimal wear.
2. Description of the Prior Art
A great variety of print actuators have been described in the literature, and many print actuators have been deployed in great numbers in a wide variety of computer printers. These print actuators must in general be small enough to be replicated for each print position in multiactuator printers, or to allow space for other mechanisms in single actuator printers. The actuator, particularly if replicated, must be inexpensive and trouble free, while maintaining tolerances sufficiently close to nominal to provide good print quality. Speed is required to accomplish printing without smudging. The usual solution is to maintain very high mechanical and electrical standards, and to drive the electromagnetic coils with very high power pulses of very short duration. These high power pulses result in a great deal of heat, concentrated on very small coil wires which are crowded into a small volume. This is very wasteful in energy, giving low print energy versus input energy efficiencies with the majority of the input energy being dissipated as heat loss. The need for an inexpensive, trouble free, effective print actuator persists, particularly for printers at the lower end of the product cost spectrum.
The following patents and publications are repesentative of the prior art:
U.S. Pat. No. 3,164,085, Hawkins, MECHANICAL LINKAGES TO ELECTRO-MAGNETS AND SOLENOIDS CONTROLLING PRINT HAMMER MECHANISMS, Jan. 5, 1965. shows a rocking lever two piece print hammer, with hammer pivot in line with the energy transfer surface and armature pivot, but not with the hammer pivot between armature pivot and energy transfer surface. This relationship, while permitting energy transfer from armature to hammer with a minimum of sliding movement, results in a bellcrank configuration of the hammer. Hawkins shows a double rocker arrangement of bell crank armature and bell crank hammer which permits the point of contact 7 in Hawkins' FIG. 2 to move along a line intersecting the pivot of the two bell cranks. This hammer configuration differs from the simple lever print hammer in that it has greater inherent mass and inherently inferior flight dynamics due to lesser power-to-velocity advantage, suffers greater damping in the bellcrank and greater energy transfer to the pivot shaft.
Hawkins does not show an end pivoted lever print hammer.
U.S. Pat. No. 3,593,657, Guzak, COMBINED PRINT HAMMER MODULE AND PRINTED CIRCUIT BOARD, July 20, 1971, shows a compact construction by which a number of print hammers are operated by individual printed circuit boards.
U.S. Pat. No. 3,266,419, Erpel et al, HIGH SPEED IMPACT PRINT HAMMER ASSEMBLY WITH RESILIENT ENERGY STORING MEANS, Aug. 16, 1966.
U.S. Pat. No. 3,630,142, Fulks, ELECTROMAGNETIC DRIVE FOR PRINT HAMMERS, Dec. 28, 1971, shows a multiple print hammer assembly in which an armature operates the linear transducer serving as an impactor.
U.S. Pat. No. 3,643,594, Pipitone, PRINT HAMMER FOR HIGH SPEED PRINTER, Feb. 22, 1972, shows an armature and print hammer suspended on a common pivot.
U.S. Pat. No. 3,919,933, Potter, HIGH SPEED PRINTER, Nov. 18, 1975, shows a multiple actuator assembly using mirror image sets of three-piece pushrod print actuators.
U.S. Pat. No. 3,924,725, Kuhn et al, DUEL ARRAY DISC PRINTER, Dec. 9, 1975, shows a disc printer in which a first alphameric set is on a first half of the disc and second alphameric set is on the second half of the disc, normally, lower case half and upper case half. The print hammer is shiftable relative to the print position from a lower case position to an upper case position.
U.S. Pat. No. 4,269,117, Lee et al, ELECTRO-MAGNETIC PRINT HAMMER, May 26, 1981, shows a one-piece whipping hammer in which the hammer of the armature is flexible.
U.S. Pat. No. 4,442,770, Dozier, PUSHROD FOR HIGH SPEED, Apr. 17, 1984, shows an improved pushrod, for an impact printer, where the pushrod wire has a soft tip at each end, using a special configuration so that the molding of the impact buttons does not require adhesives or staking.
JA Pat. No. 55-79183, Oota, PRINTING HAMMER, June 14, 1980, shows a two-piece print hammer built according to a special formular so as to provide a zero order vibrating mode of the print hammer.
JA Pat. No. 58-136469(A), PRINT MAGNET DRIVING SYSTEM, Takeda, Aug. 13, 1983, shows a two-piece print hammer in a system having a special start-up routine so that proper printing can take place from a cold start.
Lee et al, TWO-PIECE HAMMER, IBM Technical Disclosure Bulletin, Vol. 27, No. 4A, September, 1984, pp. 2090-2092; shows a two-piece armature hammer assembly, but does not align the armature pivot, the hammer pivot and the energy transfer surface.
A number of one-piece print actuators have been deployed, typified by the whipping hammer, (U.S. Pat. No. 4,269,117, Lee et al, ELECTROMAGNETIC PRINT HAMMER) in which a relatively flexible long print hammer leg and relatively large mass coil leg form an integral armature.
A number of two-piece print actuators have been deployed, in which an armature transfers energy to the print hammer directly, usually by a camming action.
A number of three-piece print actuators have been deployed, typically having a pushrod, print hammer, and armature. The pushrod transfers energy from the armature to the print hammer. The pushrod is subject to sliding friction, is subject to bending, and requires careful assembly. This in general results in a costly assembly.
The prior art does not teach nor suggest the invention, which optimizes operation and minimizes wear in a two-lever pivoted armature, pivoted print hammer, print actuator by aligning in sequence armature pivot, print hammer pivot and energy transfer surface and by controlling lever length relationships of armature and print hammer for optimum velocity advantage.